Optical pick-up apparatus and optical disc apparatus

ABSTRACT

To provide an optical pick-up apparatus and an optical disc apparatus preventing a polarization hologram from being deteriorated by incidence of laser light having a wavelength for a blue laser into the polarization hologram for a CD or a DVD, an optical pick-up apparatus includes a first objective lens  10  converging first laser light having a long wavelength and irradiating it onto a first optical disc, a second objective lens  13  disposed adjacent to the first objective lens  10,  which converges second laser light having a shorter wavelength than the first laser light and irradiates it onto a second optical disc, a standing mirror  9  allowing the first laser light to be irradiated onto the first objective lens  10  and transmitting the second laser light, and a filter film  11   g  provided between the first objective lens  10  and the standing mirror  9,  which transmits the laser light and screens the second laser light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pick-up apparatus and anoptical disc apparatus used for performing a recording operation and areproducing operation on both an optical disc such as a CD or a DVD andan optical disc for a blue laser.

2. Description of the Related Art

In an optical pick-up performing a recording operation and a reproducingoperation on an optical disc, a laser diode emitting a long wavelengthlaser such as an infrared laser or a red laser was used in the relatedart, but an optical disc apparatus performing a high density recordingoperation by using a blue laser has been practically used in recentyears.

However, in a phase when an optical disc for the blue laser and theknown CD or DVD coexist, it is proposed that a recording operation and areproducing operation on plural kinds of optical discs having differentwavelengths may be performed by the same optical disc apparatus.

Since the long wavelength laser and the blue laser are different indiameter of a spot converging on a recording surface of the optical discand in refractive index of an optical member such as an objective lensdepending on the wavelength, they cannot commonly use the same opticalsystem. Therefore, when the different optical systems for eachwavelength are provided, there is no problem in performing the recordingoperation and the reproducing operation on the plural kinds of opticaldiscs.

However, there is a difficult requirement that an optical disc apparatusmounted on an electronic apparatus such as a notebook PC of which adecrease in thickness and a decrease in size are required includes arecording and reproducing mechanism of the disc corresponding to theblue laser additionally housed in a space occupied by the known opticaldisc for the long wavelength laser. Accordingly, it is difficult toprovide the optical system for performing the recording and reproducingoperations on the disc corresponding to the blue laser in a very smallspace independently of the known mechanism. Therefore, it is proposed tosave a space by commonly using a part of the optical system.

For example, in (Patent Document 1), the optical pick-up apparatus isdisclosed which includes a plurality of light sources emitting aplurality of light beams having a plurality of different wavelengths,wherein the light beams, at least a part thereof which are emitted fromthe plurality of light sources passes through the same light path andunits converging onto different optical discs are independently provideddepending on the wavelengths.

FIG. 8 is a schematic view illustrating a basic configuration of theoptical system of the optical pick-up apparatus disclosed in (PatentDocument 1). In the figure, reference numeral 101 represents a firstlight source (the laser diode) emitting two-wavelength (infrared to red)laser light for performing a recording operation and a reproducingoperation on a CD or a DVD, reference numeral 102 represents an opticalmember transmitting outward light and reflecting inward light on areflective surface, reference numeral 103 represents a second lightsource (a blue laser diode) emitting laser light of a short wavelength(400 nm to 415 nm) for performing the recording operation and thereproducing operation of the disc corresponding to the blue laser,reference numeral 104 represents an optical member transmitting theoutward light and reflecting the inward light on the reflective surface,reference numeral 105 represents a beam splitter serving as an opticalpart having a reflective surface transmitting long wavelength laserlight and reflecting short wavelength laser light, reference numeral 106represents an optical member (a standing mirror) transmitting the longwavelength laser light and reflecting the short wavelength laser light,reference numeral 107 represents an optical member having an openingfilter for acquiring the number of openings required to correspond tothe optical disc such as the DVD (light of approximately 660 nmwavelength) or the CD (light of approximately 780 nm wavelength), apolarization hologram reacting on light of approximately 660 nmwavelength, and a ¼ wavelength plate, reference numeral 108 representsan objective lens, reference numeral 109 represents an optical disc,reference numeral 110 represents an optical member (the standing mirror)reflecting the short wavelength laser light, reference numeral 111represents an achromatic diffractive lens compensating chromaticaberration, reference numeral 112 represents an objective lens,reference numeral 113 represents a light detector receiving inward lightof a long wavelength reflected by the optical member 102, and referencenumeral 114 represents a light detector receiving inward light of ashort wavelength reflected by the optical member 104.

Basically, by this configuration, it becomes possible to perform therecording operation and the reproducing operation on the CD or the DVDcorresponding to the long wavelength laser and the optical disccorresponding to the short wavelength laser (the blue laser).

An optical pick-up apparatus using a two-wavelength laser unit for theCD or the DVD is disclosed in, for example, (Patent Document 2).

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2005-85293

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2001-307367

However, a blue laser emitted from a second light source 103 istransmitted onto an optical member 104, is reflected on a reflectivesurface of a beam splitter 105, and is transmitted onto an opticalmember 106. At this time, the blue laser is ideally transmitted onto theoptical member 106, but the blue laser of several % is reflected on thereflective surface of the optical member 106 and is incident into anoptical member 107 in actuality. As described above, the optical member107 includes optical members such as an opening filter, a polarizationhologram, and an optical member such as a ¼ wavelength plate laminatedthereon and is made of synthetic resin.

The blue laser has a shorter wavelength and larger energy than aninfrared laser or a red laser. Accordingly, when even slight light iscontinuously irradiated or accumulated irradiation time is increased,the synthetic resin constituting the optical member 107 is slowlydeteriorated for a long time, thereby decreasing a transmittance of longwavelength laser light. In particular, the polarization hologramtransmits most of outward light and changes a polarization state so thatinward light reaches a light detector 113 through a beam splitter 105and an optical member 102, and is formed of an organic thin filmpolarization material. The blue laser is continuously irradiated ontothe organic thin film polarization material and the accumulatedirradiation time is increased. Accordingly, the organic thin filmpolarization material is slowly deteriorated, thereby decreasing adiffractive efficiency serving as one of performances of thepolarization hologram.

SUMMARY OF THE INVENTION

Therefore, an object of the invention is to prevent the polarizationhologram from being deteriorated by incidence of the laser light havinga wavelength of a blue laser onto the polarization hologram for a CD ora DVD, and maintaining performance of the optical pick-up apparatus andacquiring an increase in life of an optical pick-up apparatus in anoptical pick-up apparatus commonly using a part of an optical systemwith a light source having a wavelength for the CD or the DVD and alight source having a wavelength for the blue laser.

In an optical pick-up apparatus according to an aspect of the invention,a filter transmitting laser light having a predetermined long wavelengthand screening laser light having a wavelength for a disc correspondingto a blue laser is provided in front of polarization hologramdiffracting laser light having a wavelength for a CD or a DVD bypolarization

In an optical pick-up apparatus according to the invention, a filtertransmitting laser light having a predetermined long wavelength andscreening laser light having a wavelength for a disc corresponding to ablue laser is provided in front of polarization hologram diffractinglaser light having a wavelength for a CD or a DVD by polarization,thereby preventing the polarization hologram from being deteriorated byincidence of the laser light having the wavelength for the blue laseronto the polarization hologram for the CD or the DVD, and maintainingperformance of the optical pick-up apparatus and acquiring an increasein life of the optical pick-up apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of an optical disc apparatusaccording to an embodiment of the invention.

FIG. 2 is a schematic view illustrating an optical pick-up apparatusaccording to an embodiment of the invention.

FIG. 3 is a plan view illustrating a configuration of an optical pick-upapparatus according to an embodiment of the invention.

FIG. 4 is an enlarged view of a primary part of an optical systemadjacent to an optical disc including an optical member according to anembodiment of the invention.

FIG. 5(a) is a schematic view illustrating a configuration of the knownoptical member having an only antireflective film and FIG. 5(b) is aschematic view illustrating a configuration of the optical member havinga filter film according to an embodiment of the invention.

FIG. 6(a) is a diagram illustrating wavelength characteristics such as areflectance and a transmittance of the optical member having an onlyantireflective film and FIG. 6(b) is a diagram illustrating wavelengthcharacteristics such as a reflectance and a transmittance of an opticalmember having a filter film according to an embodiment of the invention.

FIG. 7 is a graph illustrating a relation between a blue-purple lighttransmittance of a filter film having an antireflective film and areduction rate of a diffraction efficiency of a polarization hologram.

FIG. 8 is a schematic view illustrating a basic configuration of anoptical system of an optical pick-up apparatus disclosed in (PatentDocument 1).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to an embodiment of the invention, in an optical pick-upapparatus commonly using a part of an optical system with a light sourcehaving a wavelength for a CD or a DVD and a light source having awavelength for a blue laser, an object to prevent the polarizationhologram from being deteriorated by incidence of the laser light havinga wavelength of a blue laser onto the polarization hologram for the CDor the DVD, and maintain performance of the optical pick-up apparatusand acquire an increase in life of the optical pick-up apparatus.

According to an embodiment of the invention contrived to solve theproblem, the optical pick-up apparatus includes a first objective lensconverging first laser light having a long wavelength and irradiating itonto a first optical disc, a second objective lens disposed adjacent tothe first objective lens, which converges second laser light having ashorter wavelength than the first laser light and irradiates it onto asecond optical disc, an optical member allowing the first laser light tobe irradiated onto the first objective lens and transmitting the secondlaser light, and a filter provided between the first objective lens andthe optical member, which transmits the laser light and screens thesecond laser light.

Embodiments

Hereinafter, embodiments of the invention will be described withreference to the accompanying drawings.

FIG. 1 is an external perspective view of an optical disc apparatusaccording to an embodiment of the invention and illustrates a state inwhich a tray on which an optical disc is placed is drawn out from acase.

In FIG. 1, reference numeral 31 represents an optical disc apparatus,reference numeral 32 represents the case, reference numeral 32 arepresents an upper case portion, reference numeral 32 b represents alower case portion, reference numeral 33 is the tray, reference numeral34 represents an optical pick-up module, reference numeral 35 representsa rail, reference numeral 36 is a rail guide part, reference numeral 25represents a spindle motor, reference numeral 25 a represents an opticaldisc mounting portion, reference numeral 38 represents a cover,reference numeral 38 a represents an opening, reference numeral 39represents a carriage, reference numeral 40 represents a bezel,reference numeral 41 represents an eject button, and reference numeral50 represents an optical pick-up.

An optical disc apparatus 31 has a case 32 and a tray 33 movably held onthe case 32. The case 32 is pouched in combination of an upper caseportion 32 a and a lower case portion 32 b made of metal. The tray 33 isdrawn out from the opening of the case 32 or is housed in the opening ofthe case 32. An optical pick-up module 34 is mounted on the tray 33 froma rear surface thereof.

A rail guide part 36 is provided in a side portion of the tray 33 and arail 35 moves along an external surface of the rail guide part 36. Bythis configuration, the tray 33 can be drawn out from the case 32 or thetray 33 can be housed in the case 32.

The optical pick-up module 34 at least includes a spindle motor 25rotating the optical disc, a cover 38 having an opening 38 a through anouter periphery from the spindle motor 25, and a carriage 39 of whichpart is exposed from the opening 38 a. The carriage 39 is movably heldon a plurality of guide shafts provided in the optical pick-up module 34and can move close to or move off from the spindle motor 25 with a feedmotor not shown.

A bezel 40 is provided in front of the tray 33 and has a size enough toplug the opening of the case 32. A light source such as a high-powerlaser diode, various optical members, and an object lens constituting alight spot on the optical disc are mounted on the carriage 39. A circuitsubstrate is fixedly provided in an inner portion of the case 32 and asignal processing system IC or a power supply circuit is mounted on thecircuit substrate. A flexible print substrate on which circuitsubstrates not shown provided on the tray 33 are electrically connectedto each other is substantially U-shaped and an external connector isconnected to a power supply line and a signal line provided in anelectronic apparatus such as a computer. Electricity is supplied intothe optical disc apparatus 31 through the external connector, a signalreceived from an external apparatus is guided into the optical discapparatus 31, or an electrical signal generated in the optical discapparatus 31 is transmitted to the electronic apparatus. An eject button41 is provided in the bezel 40 provided on a front end surface of thetray 33 and engagement of an engagement part provided in the case 32 andthe an engagement part provided in the case 33 is released by pressingthe eject button 41, whereby the tray 33 can be drawn out from the case32 so that the optical disc can be attached and removed.

Engagement of the engagement part provided in the case 32 and theengagement part provided in the case 33 is released by pressing theeject button 41 and the tray 33 is drawn out from the case 32 so as todraw out the tray 33 when the tray 33 is housed in the case 32. When thetray 33 is drawn out by a predetermined distance, a protrusion providedin the rail guide part 36 and a protrusion provided in the rail 35contact each other and the protrusion provided in the rail 35 and aprotrusion provided in the case 32 contact each other, whereby the tray33 stops while the tray 33 is drawn out.

FIG. 2 is a schematic view illustrating a configuration of the opticalpick-up apparatus according the embodiment of the invention and FIG. 3is a plan view illustrating a configuration of the optical pick-upapparatus according to the embodiment of the invention. A side A ofdouble wave lines shown in FIG. 2 is a schematic view illustrating ashort wavelength optical unit 1 and a long wavelength optical unit 3 toa collimator lens 8 as viewed in a Z direction (an upper side of paper)shown in FIG. 3 and a side B of the double wave lines shown in FIG. 2 isa schematic view illustrating a standing mirror 9 to the optical disc 2of the optical pick-up apparatus as viewed in an R direction shown inFIG. 3.

In FIG. 2, reference numeral 1 represents a short wavelength opticalunit emitting a short wavelength laser and light emitted from a shortwavelength optical unit 1 has a wavelength in the range of 400 nm to 415nm and light having a wavelength of approximately 405 nm is emitted inthe embodiment. In general, light of the above-mentioned laserwavelength shows blue to purple colors. In the embodiment, the shortwavelength optical unit 1 is specifically described later, but the shortwavelength optical unit 1 includes a light source part 1 a emitting theshort wavelength laser, a light receiving part 1 b for signal detectionreceiving light reflected from the optical disc 2, a light receivingpart 1 c monitoring an amount of light emitted from the light sourcepart 1 a, an optical member 1 d, and a holding member (not shown)holding the constituent members at a predetermined position. The lightsource part 1 a includes a semiconductor laser element (not shown)composed of GaN or primarily composed of GaN. Light emitted thesemiconductor laser element is incident into the optical member 1d and apart of the incident light is reflected on the optical member 1 d andenters the light receiving part 1 c. Although not shown, a circuit isprovided which adjusts an intensity of the light emitted from the lightsource part 1 a to a desired intensity on the basis of an electricalsignal into which the light receiving part 1 c converts. Most of thelight emitted from the light source part 1 a is guided to the opticaldisc 2 through the optical member 1 d. Light reflected from the opticaldisc 2 is incident into the light receiving part 1 b through the opticalmember 1 d. The light receiving part 1 b converts the light into theelectrical light and generates an RF signal, a tracking error signal,and a focus error signal from the electrical signal. The optical member1 d includes a polarization hologram 1 e separating the light reflectedfrom the optical disc 2 so as to acquire the focus error signal.

In the embodiment, one short wavelength optical unit including the lightsource part 1 a, the light receiving parts 1 b and 1 c, and the opticalmember 1 d constitutes the optical pick-up apparatus so as to acquire adecrease in size of the optical pick-up apparatus, but at least one ofthe light receiving parts 1 b and 1 c may be provided separately fromthe short wavelength optical unit 1 or the optical member 1 d may beprovided separately from the short wavelength optical unit 1.

Reference numeral 3 represents a long wavelength optical unit emitting along wavelength laser. A light beam emitted from the long wavelengthoptical unit 3 is a wavelength in the range of 640 nm to 800 nm and alight beam having one kind of wavelength is singly emitted or plurallight beam having plural kinds of wavelengths are plurally emitted. Inthe embodiment, a light flux (red light: for example, corresponding tothe DVD) of approximately 660 nm and a light flux (infrared light: forexample, corresponding to a CD) of approximately 780 nm are emitted. Inthe embodiment, the long wavelength optical unit 3 is specificallydescribed later, but the long wavelength optical unit 3 includes a lightsource part 3 a emitting the long wavelength laser, a light receivingpart 3 b for signal detection receiving the light reflected from theoptical disc 2, a light receiving part 3 c monitoring an amount of lightemitted from the light source part 3 a, an optical member 3 d, and aholding member (not shown) holding the constituent members at apredetermined position. A semiconductor laser element (not shown) isprovided in the light source part 3 a and the semiconductor laserelement includes monoblocks (a monolithic structure). The (red) lightflux of approximately 660 nm and the (infrared) light flux ofapproximately 780 nm are emitted from a monoblock element. In theembodiment, the monoblock element emits two light fluxes, but each oftwo block element of the semiconductor laser element may emit one lightflux. Plural light fluxes emitted from the semiconductor laser elementis incident into the optical member 3 d and a part of the incident lightis reflected on the optical member 3 d and enters the light receivingpart 3 c. Although not shown, a circuit is provided which adjusts anintensity of the light emitted from the light source part 3 a to adesired intensity on the basis of an electrical signal into which thelight receiving part 3 c converts. Most of the light emitted from thelight source part 3 a is guided to the optical disc 2 through theoptical member 3 d. Light reflected from the optical disc 2 is incidentinto the light receiving part 3 b through the optical member 3 d. Thelight receiving part 3 b converts the light into the electrical signaland generates an RF signal, a tracking error signal, and a focus errorsignal from the electrical signal. The optical member 3 d includes apolarization hologram 3 e separating the light beam reflected from theoptical disc 2 into plural light beam and guiding the separated plurallight beams to predetermined locations of the light receiving part 3 bso as to generate a focus error signal for the CD.

In the embodiment, one long wavelength optical unit 3 including thelight source part 3 a, the light receiving parts 3 b and 3 c, and theoptical member 3 d constitutes the optical pick-up apparatus so as toacquire a decrease in size of the optical pick-up apparatus, but atleast one of the light receiving parts 3 b and 3 c may be providedseparately from the long wavelength optical unit 3 or the optical member3 d may be provided separately from the long wavelength optical unit 3.

Reference numeral 4 represents a beam shaping lens which the lightemitted from the short wavelength optical unit 1 and the light reflectedfrom the optical disc 2 pass through. It is preferable that a beamshaping lens 4 is made of glass having low deterioration caused bypassage of the short wavelength laser. In the embodiment, the beamshaping lens 4 is made of glass, but the beam shaping lens 4 may be madeof all materials which have low deterioration caused by passage of theshort wavelength laser. The beam shaping lens 4 is provided so as toremove astigmatism of the shot wavelength laser and astigmatism causedon a light path reaching the optical disc 2 from the short wavelengthoptical unit 1. Although the light reflected from the optical disc 2 maybe incident into the short wavelength optical unit 1 without passingthrough the beam shaping lens 4 for the purpose of the beam shaping lens4, the light reflected from the optical disc 2 is incident into theshort wavelength optical unit 1 through the beam shaping lens 4 in termsof an optical arrangement in the embodiment. In the embodiment, althoughthe beam shaping lens 4 is used to reduce astigmatism of the shortwavelength light, a beam shaping prism or a beam shaping hologram may beused instead of the beam shaping lens 4.

A convex portion 4 a and a concave portion 4 b are provided at both endof the beam shaping lens 4. The beam shaping lens 4 is disposed so thatthe light emitted from the short wavelength optical unit 1 enters theconvex portion 4 a and is emitted from the concave portion 4 b.

Reference numeral 5 represents an optical member. An optical member 5 isdisposed in front of the beam shaping lens 4 on the light path and isdisposed on the concave portion 4 b side of the beam shaping lens 4. Inother words, the light emitted from the short wavelength optical unit 1is incident into the optical member 5 through the beam shaping lens 4and is guided to the optical disc 2. The light reflected from theoptical disc 2 passes through the optical member 5 and the beam shapinglens 4 sequentially, and it is incident into the short wavelengthoptical unit 1. The polarization hologram is provided in the opticalmember 5 and at least has the following function. In other words, thepolarization hologram has a function of separating the light reflectedfrom the optical disc 2 into predetermined light fluxes so as toprimarily generate the tracking error signal. As described above, thepolarization hologram 1 e provided in the optical member 1 d separatesthe light reflected from the optical disc 2 into plural light fluxes soas to generate the focus error signal and the optical member 5 separatesthe light into the plural light fluxes so as to generate the trackingerror signal.

More specifically, the optical member 5 may serve as an RIM intensitycompensating filter attenuating an intensity of light in approximately amiddle portion of the short wavelength light. Further, the opticalmember 5 is divided into two. One side of the optical member 5 mayseparate the light reflected from the optical disc 2 into thepredetermined light fluxes so as to primarily generate the trackingerror signal and the other side thereof may serve as the RIM intensitycompensating filter.

Reference numeral 6 represents a relay lens which the long wavelengthlight emitted from the long wavelength optical unit 3 passes through. Arelay lens 6 includes a transparent member such as resin or glass. Therelay lens 6 efficiently guides the light emitted from the longwavelength optical unit 3 to a rear member. Since the long wavelengthoptical unit 3 can be disposed closer to a beam splitter 7 side by therelay lens 6, it is possible to acquire a decrease in size of theoptical pick-up apparatus.

Reference numeral 7 represents a beam splitter serving as the opticalmember. At least two transparent members 7 b and 7 c are provided incontact with each other in a beam splitter 7, one slope face 7 a isprovided between the transparent members 7 b and 7 c, and a wavelengthselecting film is provided on the slope face 7 a. The only wavelengthselecting film is directly formed on the slope face 7 a of thetransparent member 7 c which the light emitted from the short wavelengthoptical unit 1 penetrates and the transparent member 7 b contacts theslope face 7 a of the transparent member 7 c on which the wavelengthselecting film is formed with a contact material made of the resin orthe glass, which is interposed therebetween.

The beam splitter 7 reflects the short wavelength light emitted from theshort wavelength optical unit 1 and transmits the light emitted from thelong wavelength optical unit 3. In other words, the light emitted fromthe short wavelength optical unit 1 and the light emitted from the longwavelength optical unit 3 are guided substantially in the samedirection.

Reference numeral 8 represents a collimator lens held to be freelymovable. A collimator lens 8 is attached to a slider 8 b and the slider8 b is movably attached to a pair of support members 8 a providedsubstantially parallel to each other. A lead screw 8 c having a helicalgroove is provided substantially parallel to the support members 8 a anda protrusion inserted into the groove of the lead screw 8 c is providedat an end portion of the slider 8 b. A gear group 8 d is coupled to thelead screw 8 c and a driving member 8 e is provided in the gear group 8d. A driving force of the driving member 8 e is transferred to the leadscrew 8 c via the gear group 8 d and the lead screw 8 c rotates by thedriving force, whereby the slider 8 b moves on the support members 8 a.In other words, the collimator lens 8 can move adjacent to or move offfrom the beam splitter 7 depending on a difference in driving directionor a difference in driving speed of the driving member 8 e, and it canadjust the movement speed.

Various motors are pertinently used as the driving member 8 e, and moreparticularly, a stepping motor is preferably used as the driving member8 e. In other words, a rotation number of the lead screw 8 c isdetermined by adjusting the number of pulses transferred to the steppingmotor. As the result, a movement distance of the collimator lens 8 canbe easily set.

As described above, it is possible to easily adjust a sphericalaberration by adopting a configuration in which the collimator lens 8moves adjacent to or moves off from the beam splitter 7. In other words,since a spherical aberration of the short wavelength light can beadjusted by a position of the collimator lens 3, it is possible toeffectively perform at least one of a recording operation and areproducing operation on a first recording layer provided in the opticaldisc 2 corresponding to a short wavelength and a second recording layerhaving a depth different from the first recording layer.

The collimator lens 8 is made of the glass or is preferably made ofshort wavelength light resistant resin (resin not deteriorated or hardto be deteriorated by the short wave length light) so that the shortwavelength light and the long wavelength light incident from the beamsplitter 7 are transmitted onto the collimator 8. The collimator lens 8also transmits the short wavelength light or the long wavelength lightreflected from the optical disc 2.

In the embodiment, the collimator lens 8 is moved to the driving member8 e so as to compensate the spherical aberration of the short wavelengthlight, but the collimator 8 may be moved by other constituent membersand the spherical aberration of the short wavelength light may beadjusted using other methods.

Reference numeral 9 represents a standing mirror. A standing mirror 9includes a ¼ wavelength member 9 a acting on the short wavelength light.A ¼ wavelength plate rotating a polarization direction of light passingtwice (outward and inward) by approximately 90° is used as the ¼wavelength member 9 a. In the embodiment, the ¼ wavelength member 9 a ispinched into the standing mirror 9. A wavelength selecting film 9 b isprovided on a surface into which the light beams emitted from the units1 and 3 are incident in the standing mirror 9. The wavelength selectingfilm 9 b reflects most of the long wavelength light emitted from thelong wavelength optical unit 3 and transmits most of the shortwavelength light emitted from the short wavelength optical unit 1.

Reference numeral 10 represents an objective lens for the longwavelength laser. An objective lens 10 converges the light reflectedfrom the standing mirror 9 into the optical disc 2. In the embodiment,the objective lens 10 is used, but other converging member such as thepolarization hologram may be used. Naturally, the light reflected fromthe optical disc 2 passes through the objective lens 10. The objectivelens 10 is made of a material such as the glass or the resin.

Reference numeral 11 represents an optical member provided between theobjective lens 10 and the standing mirror 9. An optical member 11 hasthe opening filter for acquiring the number of openings required tocorrespond to the optical disc 2 such as the DVD (light of approximately660 nm wavelength) and the CD (light of approximately 780 nmwavelength), the polarization hologram reacting on the light ofapproximately 660 nm wavelength, and the ¼ wavelength member(pertinently, the ¼ wavelength plate). The optical member 11 includes adielectric multilayer film or diffractive grating opening means. Thepolarization hologram polarizes the light of approximately 660 nm(separating the light of approximately 660 nm wavelength into the lightfor the tracking error signal or the focus error signal). The ¼wavelength member rotates the polarization direction of the inward pathto the outward path of the light of approximately 660 nm wavelength andthe light of approximately 780 nm wavelength by approximately 90°.

Reference numeral 12 represents a standing mirror reflecting most of theshort wavelength light. A standing mirror 12 includes a reflective film.

Reference numeral 13 represents an objective lens. An objective lens 13converges the light reflected from the standing mirror 12 into theoptical disc 2. In the embodiment, the objective lens 13 is used, butother converging member such as the polarization hologram may be used.Naturally, the light reflected from the optical disc 2 passes throughthe objective lens 13. The objective lens 13 is made of the glass or theresin, but the objective lens 13 is preferably made of the shortwavelength optical light resistant resin (the resin which is notdeteriorated or is resistant to deterioration by the short wavelengthlight).

Reference numeral 14 represents an achromatic diffractive lens providedbetween the objective lens 13 and the standing mirror 12. An achromaticdiffractive lens 14 compensates chromatism. The achromatic diffractivelens 14 reduces chromatism caused in the optical parts which the shortwavelength light passes through. The achromatic diffractive lens 14basically includes a desired polarization hologram formed on the lens.Compensation degree of chromatism can be determined by adjusting atleast one of a lattice pitch of the polarization hologram and acurvature radius of the lens. The achromatic diffractive lens 14 is madeof resin such as plastic or cuffs. The achromatic diffractive lens 14 ispreferably made of the short wavelength light resistant resin (the resinwhich is not deteriorated or is resistant to deterioration by the shortwavelength light).

Hereinafter, a detailed arrangement of the optical system configuredabove will be described with reference to FIG. 3.

FIG. 3 illustrates an example of realization of the opticalconfiguration shown in FIG. 2. The members shown in FIG. 3 are a littledifferent from the members shown in FIG. 2 in shape and are much thesame as them shown in FIG. 2 in function.

Reference numeral 15 represents a base. The above-mentioned members arefixedly or movably attached to a base 15. The base 15 is made of metalor metal alloy such as zinc, zinc alloy, aluminum, aluminum alloy,titanium, and titanium alloy and it is preferably produced using adie-cast manufacturing method.

The base 15 is movably attached to shafts 21 and 22 disposedapproximately parallel to each other and reciprocates by rotation of ascrew shaft not shown. A spindle motor 25 rotating the optical disc 2 isprovided on the base 5.

The short wavelength optical unit 1, the long wavelength optical unit 3,the beam shaping lens 4, the optical member 5, the relay lens 6, thebeam splitter 7, the support member 8 a, the lead screw 8 c, the geargroup 8 d, a driving member 8 e, and the standing mirrors 9 and 12 areadhered to the base 15 by using organic adhesive such as light cure typeadhesive or epoxy adhesive or by using metal adhesive such as solderingor lead-free soldering, or they are attached thereto by methods such asscrewing, fitting, and press-fitting.

The lead screw 8 c and the gear group 8 d are rotatably attached to thebase 15.

Reference numeral 17 represents a suspension holder. A suspension holder17 is attached to the base 15 through a yoke member not shown by usingvarious adherence methods. The lens holder 16 and the suspension holder17 are coupled through a plurality of suspensions 18. The lens holder 16is supported on the base 15 so as to be movable by a predeterminedrange. The objective lenses 10 and 13, the optical member 11, and theachromatic diffractive lens 14 are attached to the lens holder 16. Theobjective lenses 10 and 13, the optical member 11, and the achromaticdiffractive lens 14 move with movement of the lens holder 16.

Since the standing mirror 9 is inclined to a light flux which is emittedfrom the short wavelength optical unit 1 and passes through the beamsplitter 7 or the collimator lens 8, the light flux emitted from theshort wavelength optical unit 1 is refracted and moves off from theobjective lenses 10 and 13 by a predetermined distance when it passesthrough the standing mirror 9.

The objective lens 10 and the objective lens 13 having an axialthickness larger than the objective lens 10 are sequentially arranged ina proceeding direction of the light which is emitted from the shortwavelength optical unit 1 or the long wavelength optical unit 3 andpasses through the beam splitter 7 or the collimator lens 8.

Since the light flux may not be screened by the objective lens 13 or theachromatic diffractive lens 14, even though the lens holder 16 drives upand down by the arrangement of the objective lenses 10 and 13, it ispossible to acquire a decrease in thickness of the optical pick-upapparatus.

FIG. 4 is an enlarged view of a primary part of the optical systemadjacent to the optical disc including the optical member according tothe embodiment of the invention. The optical member 11 includes anantireflective film 11 b formed on a lower surface of a first glasssubstrate 11 a and the polarization hologram 11 c formed on an uppersurface thereof, and a ¼ wavelength plate 11 e formed a lower surface ofa second glass substrate 11 d and an antireflective film 11 f formed onan upper surface thereof laminated. In the embodiment, a filter film 11g is formed on a surface of the antireflective film 11 b. The filterfilm 11 g transmits the laser light of the wavelength for the CD or theDVD and screens the laser light of the wavelength for the disccorresponding to the blue laser.

FIG. 5(a) is a schematic view illustrating a configuration of the knownoptical member having the only antireflective film. FIG. 5(b) is aschematic view illustrating a configuration of the optical member havingthe filter film of the according to the embodiment of the invention.FIG. 6(a) is a diagram illustrating wavelength characteristics such as areflectance and a transmittance of the known optical member having theonly antireflective film. FIG. 6(b) is a diagram illustrating wavelengthcharacteristics such as a reflectance and a transmittance of the opticalmember having the filter film according to the embodiment of theinvention.

As shown in FIG. 5(a) and Table 1, the known optical member 11 includesthe antireflective film 11 b composed of thin films 1 to 4 made of Ta₂O₅and SiO₂ alternatively laminated, which is provided on the lower surface(the standing mirror 9 side) of the glass substrate 11 a. As shown inFIG. 6(a), the optical member 11 transmits (a curve T) light of awavelength in the range of 640 nm to 810 nm for the CD or the DVD andtransmits (a curve R) light of the other wavelength. However, since theoptical member 11 is not designated to screen the laser light of thewavelength for the blue laser in the range of 400 nm to 415 nm,screening by the antireflective film 11 b is not sufficient even thougha part of the laser light for the blue laser reflected by the standingmirror 9 is incident thereto. TABLE 1 AP Film Constitution RefractiveFilm thickness Material index (nm) Substrate Glass (BK7 1.5215 Thin film1 Ta₂O₅ 2.2389 47 Thin film 2 SiO₂ 1.4754 42 Thin film 3 Ta₂O₅ 2.2389 64Thin film 4 SiO₂ 1.4754 74

Therefore, as shown in FIG. 5(b), the filter film 11 g is furtherlaminated on the surface of the antireflective film 11 b, therebyscreening the laser light of the wavelength for the blue laser. In theembodiment, thin films 5 to 16 are laminated as the filter film 11 g.Materials, refractive indexes, and film thicknesses of the thin films 1to 16 are exemplified in Table 2. As shown in FIG. 6(b), it is possibleto reduce a transmittance in the range of 400 nm to 415 nm to 1% or lessby a multilayer configuration constituted by 16 layers. TABLE 2 AP FilmConstitution Film Refractive thickness Material index (nm) SubstrateGlass 1.5215 (BK7 Thin film 1 Ta₂O₅ 2.2389 47 Thin film 2 SiO₂ 1.4754 42Thin film 3 Ta₂O₅ 2.2389 64 Thin film 4 SiO₂ 1.4754 74 Thin film 5 Ta₂O₅2.2389 38 Thin film 6 SiO₂ 1.4754 78 Thin film 7 Ta₂O₅ 2.2389 50 Thinfilm 8 SiO₂ 1.4754 54 Thin film 9 Ta₂O₅ 2.2389 56 Thin film 10 SiO₂1.4754 51 Thin film 11 Ta₂O₅ 2.2389 45 Thin film 12 SiO₂ 1.4754 86 Thinfilm 13 SiO₂ 2.2389 34 Thin film 14 Ta₂O₅ 1.4754 74 Thin film 15 SiO₂2.2389 52 Thin film 16 SiO₂ 1.4754 139 Air 1

FIG. 7 is a graph illustrating a relation between a blue-purple lighttransmittance of the filter film including the antireflective film and areduction rate of a diffraction efficiency of the polarization hologram.This figure illustrates the reduction rate of the diffraction efficiencyof a DVD inward light of the DVD polarization hologram 11 c after arecording operation is performed for 1,000 hours by irradiating theblue-purple light (the range of 400 nm to 415 nm) onto a surface of thedisc at a light intensity of 12 mW. It is necessary to set theblue-purple light transmittances of the antireflective film and thefilter film to 5% or less so as to suppress the reduction rate to 10% orless.

The blue-purple transmittance of the known thin films 1 to 4 was about80%, but the transmittance becomes 5%, thereby meeting a requiredcondition by formation of the thin films 1 to 10. The transmittance ofthe thin films 1 to 16 becomes 1% which is a sufficient value.

The antireflective film 11 b and the filter film 11 g are formed of twokinds of materials alternatively laminated. The thicknesses of the filmsand the number of layers are acquired by combining a predeterminedcalculating formula with an actual measurement value. Values shown inTable 1 and Table 2 are only examples.

In the embodiment, an example is described in which Ta₂O₅ and SiO₂ whichare combinations of two dielectric substances having differentrefractive index are used as the materials of the thin film constitutingthe antireflective film 11 b and the filter film 11 g, but may be usedNb₂O₂ and SiO₂ or TiO₂ and SiO₂ which are combinations of materialshaving different refractive indexes may be used.

In the embodiment, the example is described in which the filter film 11g is laminated on the antireflective film 11 b of the optical member 11,but the present invention can be performed when a filter serving as anindependent optical member is provided between the optical member 11 andthe standing mirror 9.

This application is based upon and claims the benefit of priority ofJapanese Patent Application No 2006-117606 filed on Jun. 4, 1921, thecontents of which are incorporated herein by reference in its entirety.

1. An optical pick-up apparatus, comprising: a first objective lensconverging first laser light having a long wavelength and irradiating itonto a first optical disc; a second objective lens disposed adjacent tothe first objective lens, which converges second laser light having awavelength shorter than the first laser light and irradiates it onto asecond optical disc; an optical member allowing the first laser light toprogress toward the first objective lens and transmitting the secondlaser light; and a filter provided between the first objective lens andthe optical member, which transmits the first laser light and screensthe second laser light.
 2. The optical pick-up apparatus according toclaim 1, wherein the second laser light is laser light having awavelength used for a disc corresponding to a blue laser.
 3. The opticalpick-up apparatus according to claim 1, wherein the second laser lightis laser light having a wavelength in the range of 400 nm to 415 nm. 4.The optical pick-up apparatus according to claim 1, wherein apolarization hologram changing a path of light reflected from the firstoptical disc and separating it into light for sensor detection isprovided between the first objective lens and the optical member, andwherein the filter is provided between the optical member and thepolarization hologram.
 5. The optical pick-up apparatus according toclaim 1, wherein a polarization hologram changing a path of lightreflected from the first optical disc and separating it into light forsensor detection is provided between the first objective lens and theoptical member, and wherein the filter is provided at the optical memberside of the polarization hologram.
 6. The optical pick-up apparatusaccording to claim 1, wherein the first laser light is laser lighthaving a wavelength in the range of 640 nm to 810 nm.
 7. The opticalpick-up apparatus according to claim 1, wherein the first laser light islaser light for a DVD or a CD.
 8. The optical pick-up apparatusaccording to claim 1, wherein the filter transmits 95% or more of thefirst laser light and screens 95% or more of the second laser light. 9.The optical pick-up apparatus according to claim 1, wherein the filteris a multilayer film and includes at least a Ta₂O₅ layer and a SiO₂layer.
 10. The optical pick-up apparatus according to claim 9, whereinthe filter includes at least the Ta₂O₅ layer and the SiO₂ layeralternatively laminated and the number of layers is in the range of 10to
 16. 11. The optical pick-up apparatus according to claim 1, whereinthe filter is a multilayer film and includes at least an Nb₂O₂ layer anda SiO₂ layer.
 12. The optical pick-up apparatus according to claim 11,wherein the filter includes at least the Nb₂O₂ layer and the SiO₂ layeralternatively laminated and the number of layers is in the range of 10to
 16. 13. The optical pick-up apparatus according to claim 1, whereinthe filter is a multilayer film and includes at least a TiO₂ layer and aSiO₂ layer.
 14. The optical pick-up apparatus according to claim 13,wherein the filter includes at least the TiO₂ layer and the SiO₂ layeralternatively laminated and the number of layers is in the range of 10to
 16. 15. An optical disc apparatus, comprising the optical pick-upapparatus according to claim 1.